Aromatic aldehydes or acids (for example, benzaldehyde, terephthalic acid, etc.) are important industrial chemicals. They have excellent resistance against heat and hydrolysis and are increasingly demanded in pharmaceutical industry, essence and perfume industry, plastics industry, polyester industry, special fiber industry and paint industry. Generally, the aromatic aldehydes or acids are industrially manufactured through air oxidation of benzene homologs (for example, methylbenzene, dimethylbenzene, etc.), and the manufacturing procedure can be divided into two processes: oxidation and rectification. The exhaust gas generated in the oxidation process constitutes a major source of pollution throughout the whole manufacturing procedure. On the one hand, the oxidation process requires a certain level of pressure and considerably high temperature; on the other hand, the oxidation process of hydrocarbons releases a certain amount of heat; therefore, the temperature of the discharged exhaust gas reaches as high as 120-280° C. Meanwhile, since most reactors are working under pressurized conditions, the exhaust gas discharged in the oxidation process is accordingly pressurized to some degree. Normally, the pressurized exhaust gas is about 0.3-2.8 MPa. Under such a pressurized and hot condition, the exhaust gas generated in the oxidation process unavoidably contains various amounts of reagents, solvents and products. In order to obtain up-to-standard discharge of the exhaust gas, these organic components must be removed from the exhaust gas. Currently, the process most frequently adopted in treating the exhaust gas generated in the oxidation process is as follow: firstly, trapping organic components in the exhaust gas by means of condensation realized by a condenser; next, adopting wet or dry absorption (adhesion) to remove the organic components before discharging the exhaust gas into the atmosphere. In order to conserve energy resources, the condensation process adopted by most manufacturers is realized not by refrigerating fluid, but simply by cooling water. Therefore, the temperature of the cooled exhaust gas is still as high as 50-100° C. The content of the organics contained therein still remains high. This consequently complicates the follow-up process of the wet or dry absorption (adhesion), particularly those dry absorption (adhesion) processes using active carbon, because the absorption bed formed by active carbon will soon turn saturated if the content of the organics in the exhaust gas remains high, which means that the active carbon bed must be frequently regenerated. This not only consumes a lot of energy, but also results in secondary pollution and waste of organic resources during the regeneration process.
In addition, since the exhaust gas generated in the oxidation process is pressurized, the direct discharge into the atmosphere will cause not only noise pollution but also waste of useful pressure energy.
Therefore, it is of necessity to improve the existing processes for treating the exhaust gas generated in the air oxidation of (aromatic) hydrocarbons.